1. Field of the Invention
The present invention relates to vehicle suspension systems and more particularly to axle stabilizing systems.
2. Description of the Problem
Truck suspension systems provide isolation of passengers and cargo from road shock while keeping the vehicle stable and preserving operator control. These objectives are met using combinations of springs, motion damping devices and auxiliary axle positioning elements. Achieving acceptable levels of performance, while supporting the vehicle's weight over a wide range of vehicle load conditions, is preferably achieved with a mechanically simple, compact and light weight suspension system.
The central element of any suspension system is the spring, and the four most popular, basic types of suspension systems used on trucks are categorized by the spring used, i.e.: leaf spring systems; equalizing beam systems; torsion bar systems; and air spring systems. Hybrid combinations of these are also used.
Air spring based systems have recently gained in popularity and have been applied to both steering and non-steering axles as well as driven and undriven axles. In an air spring based system, air bellows are positioned with respect to an axle and a vehicle frame to support the frame from the axle. Air spring suspensions give excellent load and vibration isolation by eliminating the interleaf friction found in traditional multiple leaf spring designs and, in some systems, by allowing active control of the spring rate. In addition, an air spring usually has a lower deflection rate than a leaf spring exerting the same force, giving the system greater capacity for absorbing shocks for a given displacement between the axle and the frame. Air spring pressure can be adjusted to compensate for vehicle load changes by adding air to or exhausting air from the spring. This aspect of the springs also benefits other suspension design objects, since by adding or exhausting air the vehicle height need not vary with load or positioning of the load.
A drawback of non-hybrid air spring suspension systems, especially when compared with leaf spring systems, is that they require more auxiliary stabilization to maintain the proper location and attitude of the axle with respect to the vehicle and to prevent excessive vehicle roll. Absent stabilization, air springs will extend to their maximum lengths or widths in the direction of least resistance and can cause an unevenly loaded vehicle to fall over to one side, while full leaf springs, because of twin points of connection to the vehicle frame both fore and aft of the axle, are partially self-stabilizing and provide better directed support.
Auxiliary stabilization may be directed to controlling one or more specific types of undesired movement of a vehicle or axle. To some extent, the control of one type of movement may be more readily accomplished by trading off control of another type of movement. Some auxiliary stabilizing elements can even promote certain types of undesired vehicle body or axle movement while achieving control of some other movement. Among the problems to be controlled are vehicle roll occurring during cornering, suspension expansion adjacent a driven axle on acceleration (acceleration lift), and lateral deflection of the axle, particularly during turning. Some auxiliary stabilizing systems produce axle caster changes with vertical motion of an axle.
Countering some or all of these problems is preferably obtained using auxiliary components which are not excessively complex, bulky or heavy, and which allow the full capacity of the air springs to be utilized. It would be further advantageous if the auxiliary elements provided a base for positioning an air spring.